I had gotten the screenplay book from my local library a couple years back and created a sub file from that for an Xvid version floating around. I don't speak Japanese or Mandarin (so as long as the actors stuck to the script then it's fine).
The only real discrepancy was the first scene in Takeshi's office. In the U.S. version (which is of course subbed for that scene), they either went off script, the scene was cut, or the subtitles were over simplified. I put it back to the original script's version for story purposes. Most importantly they refer to themselves as Yakuza now which I don't actually think is mentioned at any other point in the movie. You otherwise have the impression they work for the corporation and are not freelance thugs. Since Yakuza is Japanese you should hear them say it, but I don't, so again, my sub file takes liberties, but I am a big Gibson fan and felt his words were more important.
If anyone is interested in comparing the subs, here's mine:
http://rapidshare.de/files/14776922/JM_Johnny_Mnemonic_103min_jap_Version.sub.html